How to implement expansion? (Humankind)

Expansionist civilizations have two features - they can pass through the territory of foreign cities without a contract (outposts are already considered neutral territory) and can annex foreign districts, even those belonging to a foreign city. It is impossible to annex during the war (in fact, it is pointless) and the ability is applied to the administrative centers of districts (territories)

you need to approach someone else's outpost or city in peacetime. select a detachment, press the expansion button from above and click on the city / outpost (like with the left button), the timer will start counting moves, it is better not to touch this detachment, not to divide or replenish, otherwise everything may be reset